1. Field of the Invention
The present invention relates to a method for driving a retransmission timer in a mobile telecommunications system using a radio link protocol (RLP).
2. Description of the Related Art
As well known to those skilled in the art, a radio link protocol employed in a general CDMA mobile telecommunications system utilizes an automatic repeat request (ARQ) technique based on a non-acknowledgement (NAK) to recover errors or erroneous frames generated in a wireless channel. The terms used in this application are as follows.
A control frame includes SYNC, SYNC/ACK, ACK, and NAK frames. The SYNC, the SYNC/ACK, and the ACK frames are used to initialize a RLP (3 Way Handshake Method). The NAK frame is used to request retransmission.
A data frame transmits data of an upper layer. The data frame includes a new data frame and a retransmitted frame. The new data frame receives data of the upper layer and the retransmitted frame retransmits the data in response to the NAK. An idle frame is transmitted in the case when no control frame or data frame is transmitted or when the control frame and the data frame can not be transmitted. An eraser frame is a frame broken or disrupted by noise on an air channel. A retransmission timer waits for arrival of the retransmitted frame after transmitting the NAK. The NAK ROUND means a time period until the retransmission timer is operated after transmitting the NAK, the retransmitted frame is received and the retransmission timer expires. In case that the NAK ROUND=2, a second NAK ROUND is performed in the case that the retransmitted frame is not received in a first NAK ROUND. A round trip delay (RTD period) is a value obtained in the RLP initialization and indicates a time taken in transmitting a RLP frame made in a transmitting RLP to a receiving RLP and returning again.
The order of priority of RLP for transmitting frames is as follows: First, the control frame (SYNC frame, SYNC/ACK frame, ACK frame), second, the retransmitted data frame; third, the new data frame; and fourth, the idle frame.
FIG. 1 is a timing diagram illustrating the operation of a conventional retransmission timer. The conventional ARQ technique will be briefly described with reference to FIG. 1. If there is an error in a data frame transmitted from a transmitter RLP, a receiver RLP requests the transmitter RLP to retransmit the frame. At this moment, the receiver RLP not only requests the retransmission, but also drives a retransmission timer. The retransmission timer is set to round trip delay (or a round trip time (RTT), referred to hereinafter as RTD) period plus a spare period.
The receiver RLP keeps decreasing the value of the retransmission timer until the corresponding frame is received. When a control frame, retransmitted frame or eraser frame is received while the value of the retransmission timer is being decreased, the receiver RLP will hold the retransmission timer.
Referring to FIG. 1, since the receiver RLP has received the retransmitted frame in response to the control frame (an NAK frame in FIG. 1) or a previous NAK frame, the receiver RLP holds the retransmission timer. Accordingly, an expiration time of the retransmission timer is lengthened by a time period as long as a period that is indicated with a dotted line. Note that frames received when the value of the retransmission timer is in the RTD period are frames that the transmitter RLP has transmitted irrespective of an NAK frame transmitted from the receiver RLP. Therefore, holding the retransmission timer when the value of the retransmission timer is in the RTD period causes an unnecessary delay in the expiration time of the retransmission timer.
The unnecessary delay as described above causes problems in that data transfer to the upper layer is delayed and the processing speed of applications is reduced.